As described in previous reports, a hemagglutination inhibition test suitable for the diagnosis of pregnancy in macaques has been developed in this laboratory. The Subhuman Primate Pregnancy Test Kit, distributed under the aegis of the Contraceptive Development Branch, Center for Population Research, NICHD, has been sent to primate facilities all over the world. To date, more than 1100 kits have been delivered, sufficient for more than 55,000 pregnancy tests. In order to realize the full potential of this kit, we have undertaken a series of studies to determine the interval for most reliable detection of urinary chorionic gonadotropin from a variety of primates including: macaques (Rhesus and Cynomolgus), baboons, marmosets, chimpanzees, organgutans, squirrel monkeys, tamarins, and owl monkeys.